Debra Reiss, daughter of REISS clothing store founder David Reiss, has died at the age of 34Getty

Debra Reiss, the heiress to the £125m Reiss fashion empire, has died. The 34-year-old daughter of mogul David Reiss, who was pregnant with her second child, passed away suddenly in Los Angeles. She had been suffering from a long-term illness.

"This is a personal matter for David Reiss and his family," said a spokesman for the Reiss family, the Telegraph reported. "Safe to say that the thoughts of everyone at Reiss are with David and his family at this sad time."

Reiss, who served as the company's brand director, is said to have been working in LA at the time of her death. No further details of what caused her death were made available.

Following news of her passing, friend flocked to social media to express their grief and share their condolences. One wrote: "Just woke up to this tragic news and just could not believe it. Dee you will be greatly missed. I will cherish all the fun moments we shared together. My thoughts are with your family Zane and beautiful baby Scarlett."

Another added: "Heaven has gained another special angel and her baby. Feel sick to have learnt of such sad news. Thinking of her family at such a horrendous time."

David, 72, founded the company in 1971 after taking over his father's East End gentleman's outfitters. He turned the fashion chain into a worldwide retail giant loved by scores of A-list celebrities. Kate Middleton, the Duchess of Cambridge, wore a white £159 Reiss dress for her official engagement photograph, taken by Mario Testino in January 2011. As a result of the 'Kate effect' the brands has seen sales surge.

Reiss is survived by her one-year-old daughter Scarlett as well as her partner Zane William.